Method of preparing bright yellow colored sulfides



July 22,1958

METHOD OF PREPARING-BRIGH'I YELLOW COLORED SULFIDES,

J. VW. LEFFORGE original Fixed July 23. 1954 AGENT.

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wilnite arent hice METHOD @F PREPARXNG BRIGHT YELLOW COLORED SULFlDESJohn W. Lefiorge, liynneld Center, Mass., assigner to Monsanto ChemicalCompany, St. Louis, Mo., a corporation of Delaware Original application.luly 23, 1954, Serial No. 445,349. Divided and this application May2li, 1957, Serial No. 660,407

7 claims. (ci. zs-zos) This invention relates to phosphorusy sulfidesand to an improved method of producing same.

l-leretofore, phosphorus sulfides have been prepared continuously byintroducing phosphorus and sulfur with agitation into a molten heel ofphosphorus sullide and reacting these materials in the proportionscalculated to yield the desired product. ln carrying out this reaction,the exothermic heat is absorbed by the molten heel of phosphorus sulfideand thereby transferred to a suitable heat exchanging material orsurface. The product of this reaction is withdrawn continuously from thereaction zone, flaked on chill rolls and then converted into a powder bygrinding in a hammer mill or equivalent pulverizing device. T his methodprovides a means of producing phosphorus sulfides continuously but issubject to certain disadvantages which render the method and productcommercially unattractive.

For example, this method invariably yields darkly colored products as aresult of the accumulation of impurities including those derived fromthe raw materials and the metal equipment. The color of these materialscan be improved to some extent by distillation, but until thedevelopment of the invention disclosed and claimed in the applicationSerial No. 445,329, filed July 23, 1954, which has issued as Patent No.2,794,705, June 4, 1957, such treatment has involved the use ofadditional heat and equipment, all of which Iadd substantially to theoverall cost of manufacturing these products.

Another disadvantage of this method is that if the phosphorus and`sulfur feeds vary from a predetermined rate, the resulting product hasa heterogeneous composition due to the presence of excess reactants orthe formation of phosphorus sulfdes other than the one desired.

in an application Serial No. 445,329, filed July 23, i954, assigned tothe same assignee as the instant application, a method of producingphosphorus suldes of improved coloris disclosed and claimed. lnaccordance with this method phosphorus and sulfur are introducedcontinuously into a boiling mass of phosphorus sulfides so as to effecta continuous reaction between the phosphorus and sulfur and continuousdistillation of the reaction product, simplicity of equipment, colorimprovement of product and product uniformity, this method represents asubstantial advance in the art over the method previously describedherein. However, it is not possible by this method to produce aphosphorus sulfide such as phosphorus pentasulfide of the desired yellowcolor for all of its numerous applications since it invariably yields ayellow product with a greyish cast. Thus, while this method yieldsproducts having a color which adapt lit for many applications, there arecertain ones such as the oil additive art in which it is not onlydesirable but essential that the phosphorus sulfide have a bright canaryyellow color. Moreover, such a color is quite desirable from thestandpoint of customer appeal and'saleability of the product.

Therefore, it is the primary object of the instant inven- From thestandpoint of economy of operation,

tion to provide a method of producing phosphorus sulfdes of uniformcomposition, which overcomes the disadvantages outlined above. Morespecifically it is an object of the instant invention to provide aneconomically and commercially feasible method of producing continuouslyphosphorus sulfides having a bright canary yellow color. Other objectsand advantages will become apparent to tho-se skilled in the art as thedescription of the invention proceeds. l

I have developed an economically and commerciallyr feasible method ofmaking phosphorus suldes having a bright canary yellow color, whichrepresents a substantial advance in the art over the methods describedearlier herein. ln accordance with the preferred embodiment of thismethod, phosphorus and sulfur are introduced continuously into a heel ofboiling phosphorus sulfide contained in a combined reactor and stillwherein the exothermic heat of the phosphorusasulfur reaction effectscontinuous distillation of the resulting reaction product.Simultaneously with the phosphorus-sulfur reaction, boric oxide isintroduced continuously into the heel of boiling phosphorus sulfide soas to effect improvement in the color of the reaction product.

The distillate obtained as a result of the phosphorussulfur reaction isconveyed continuously to a hot condenser where the phosphorus sulfidevapor is condensed substantially completely while the uncondensed gasesand phosphorus sulfide vapors are vented to the atmosphere. Thecondensed liquid .phosphorus sulfide is cooled further and fedcontinuously onto a chill roll which solidifies and breaks up theproduct into flakes continuously. If desired, the phosphorus sulfidefrom the combined reactor and still may be cooled in the condenser to asafe operating temperature and fed continuously onto the chill roll;After leaving the chill roll, the llakes are ground continuously into apowder by means of a hammer mill or an other equivalent pulverizingdevice.

As an alternative to this method, the product from the combined reactorand still, without treatment with boric oxide, is condensedcontinuously'and subjected to combined distillation and treatment withboric oxide until the product has been converted to the desired brightcanary yellow color.

As a further alternative to this method, the phosphorus sulfur reactionproducts prepared by the methods of the prior art are subjected tocombined distillation and treatment with boric oxide until the desiredbright canary yellow color is obtained.

Stated broadly, the boric oxide is introduced into the phosphorussulfide at a rate or in an amount sufficient to yield the desired yellowcolor. More specifically, the boric oxide is introduced at a rate of aneffective amount up to aboutL 5% by weight of the phosphorus sulfide.

For a more complete understanding ofthe improved method of makingphosphorus sulfides, reference is made to the accompanying flow sheetwhich constitutes part of The combined reactor and still 5 includes astill pot and in communication therewith Ia packed column containingporcelain Berl saddles, Pyrex glass rings and wool 0r equivalentmaterials. provided with an outlet line S for discharging still bot-ytoms therefrom and a discharge line 9 for conveying the distilledphosphorus sulde vapors from the packed col- This combined reactor andstill isy umn setion (not shown) of the still to a hot condenser it isalso equipped with a line 5 for introducing boric oxide into the heel ofphosphorus sulfide in the combined reactor and still 5.

The condenser 10 is provided with a jacket 11 having an inlet line 12for introducing a heat-exchanging mediumat a temperature of about 300 C.and an outlet line 13 for discharging the heat-exchanging medium at atemperature of about 305 C. from the jacket. VThe condenser is alsoequipped with a vent line 14 for discharging any inert uncondensable gasand traces of phosphorus sulfide from the system, and a take-ofi line 1Sfor conducting the condensed liquid phosphorus sulfide to a cooler 16.

The cooler 16 is provided with a jacket 17 having an inlet line 18 forintroducing a heat-exchanging medium at a temperature of about 300 C.and an outlet line 19 for conducting thevheat-exchanging medium at atemperature of about 305 C. from the jacket 17. In addition, the cooler16 is equipped with a discharge line 20 for conveying the cooledphosphorus sulfide into an enclosed chill wheel 21.

The chill wheel 21 is cooled by means of water or another suitablemedium introduced by line 22 and discharged therefrom by line 23; inaddition, in order to avoid combustion of the phosphorus sulfide beingflaked, it is blanketed by` means of an inert gas such as nitrogen orcarbon dioxide, etc. which is introduced by line 24 into the enclosuretherefor (not shown) and discharged therefrom by means of line 25. Thischill wheel 19 is provided with lan outlet line 26 through which theflaked phosphorus sulfide is conveyed to a grinding mill 27 Where theflakes are ground to a finely divided state.

The grinding mill 27 is purged by means of an inert gas such as nitrogen`or carbon dioxide, etc. which enters the mill by Vline 2@ and leaves byline 29, the purging being done as a precautionary measure to avoidcombustion of the phosphorus sulfide. This grinding mill is providedwith -a line 30 for conveying fines to a dust collector 31 from which aportion of the inert purging gas is vented into the atmosphere by line32. The grinding mill 27 is further provided with a line 33 forconveying the final product to the packaging plant 34.

The following :specific example illustrates the method of carrying outthe instant invention employing the system illustrated in theaccompanying drawing.

Liquid phosphorus and liquid sulfur were continuously charged undernitrogen pressure into a heel of phosphorus pentasulde in substantiallythe proportions required to yield the pentasulfide and a yellowish greyproduct was collected continuously as a distillate. Then, the feeding ofphosphorus and sulfur was discontinued and the distillation continued bythe external application of heat. No improvement in color of the productwas obtained.

Approximately 1% by weight (basis heel of phosphorus penta-sulde) ofboric oxide was added to the heel and the distillation continued for aperiod of about 3%: hour. The phosphorus pentasulfide product recoveredfrom the operation had a bright canary yellow color, thus demonstratingthe effectiveness of boric oxide in improving the color of this product.

In like manner phosphorus heptasulfide and phosphorus sesquisulfidehaving a bright yellow color can be produced in a continuous manner bycontinuously feeding boric oxide and the reactants in the proportionsrequired to yield these products and by operating at a temperatureequivalent to the boiling points of the heptasulide and sesquisuhide,respectively, at the operating pressure.

In the production of phosphorus pentasultide in accordance with theinstant invention, phosphorus and sulfur are continuously fed to acombined reaction and distillation zone where they are reacted togetherin a heel of the reaction product and at a temperature at leastequivalent to the boiling point of the reaction product at the operatingpressure. When operating at atmospheric pressure, the reactiontemperature used in the formation of phosphorus pentasulfide should fallsubstantially in the range of about 505 C. to 525 C., whereas in theproduction of phosphorussesquisulfide and phosphorus heptasulfide, thereaction temperature should fall within the ranges of from about 400 C.to aboutv 420 C. and from about 520 C. to about 535 C., respectively.

The reactants are introduced continuously into the heel of phosphorussulfide `at a rate producing a reaction temperature at least equivalentto the boiling point of the phosphorus sulfide, thus insuring continuousdistillation `of this product substantially as rapidly as it is formed.If desired, the reaction heat may be supplemented by the application ofexternal heating means to the combined reactor and still.

In the production of phosphorus sesquisulfide or phosphorusheptasulfide, the heat of reaction in excess of that required fordistillation is dissipated in the condenser by using a distillation rategreater than the production rate and permitting a portion of thecondensate to return from the condenser to the reactor still pot and byits cooling action maintain the desired temperature and production rate.

Boric oxide is introduced continuously into the heel of the phosphorussulfide simultaneously with the phosphorus and sulfur at a ratesufficient to produce a product having the desired bright yellow color.In producing a bright yellow phosphorus pentasulfide, boric oxide isintroduced into the heel of phosphorus pentasulfide with phosphorus andsulfur at a rate sufficient to provide the desired color improvement,but not to exceed about 5% by weight of the phosphorus and sulfur.

Somewhat lower feed rates for the additive can be used in the productionof a bright yellow colored phosphorus sesquisulfide or phosphorusheptasulfde since these products do not present a color improvementproblem that is as serious as is encountered in the manufacture ofphosphorus pentasuldde.

Instead of introducing the boric oxide into the heel of phosphorussulfide, the distilled product may be condensed and then subjected tocombined distillation and treatment with the boric oxide to form a lightcolored product.

The product leaving the combined reaction and distillation zone iscooled to condense the phosphorus sulde, the temperature used varyingwith the particular phosphorus sulde being produced. In the case ofphosphorus pentasulfide, the product from the combined reaction anddistillation zone is cooled to a temperature of about 500 C. or to alower temperature above its solidification point to effect substantiallycomplete condensation of the phosphorus pentasulfde.

The condensed phosphorus pentasulfide at a temperature of about 500 C.flows into a cooler where it is cooled to about 300 to 350 C. However,this temperature is not fixed since it varies with the phosphorussulfide being produced, the only limitation being that the liquidphosphorus sulfide should not be coiled to a temperature preventing freeflow thereof onto the chill wheel. This cooling step may be omitted ifthe product is cooled to a safe operating temperature in thecondensation zone.

The liquid phosphorus sulfide is discharged continuously from thecondenser or cooler onto a chill wheel and converted into fiakes whichare introduced continuously into a grinding mill where they are groundto a finely divided state.

The flaking and grinding operations are preferably carried out in thepresence of a dry inert atmosphere, but the invention is by no meansrestricted thereto since this is merely` a desirable precautionarymeasure designed to prevent decomposition of the product by air andmoisture.

The products of the instant invention are suitable for use in organicsynthesis and in a number of commercial applications such asanticorrosive agents and antioxidants for oils, and in the manufactureof extreme-pressure lubricants, match compositions and vulcanizedrubber.

This application is a division of my copending application Serial Number445,349, led July 23, 1954.

I claim:

l. A method of preparing bright yellow colored phosphorus suldes whichcomprises introducing boric oxide into a mass of darkly coloredphosphorus sulfide, and subjecting the resulting product to distillationto separate said phosphorus sullide in the form of a product having abright yellow color, said boric oxide being employed in an amountsuicient to produce said color improvement.

2. A method of preparing bright yellow colored phosphorus pentasuldewhich comprises introducing boric oxide into a mass of darkly coloredphosphorus pentasulde and subjecting the resulting product todistillation to separate said phosphorus pentasullide in the formof aproduct having a bright canary yellow color, said boron oxide beingemployed in an amount suflicient to produce said color improvement.

3. The method of claim 2, wherein 1 percent by weight, based on the heelof phosphorus pentasulde, of boric oxide is employed.

4. A method of preparing bright yellow colored phosphorus suldes whichcomprises continuously introducing phosphorus, sulfur and boric oxideinto a boiling mass consisting of phosphorus sulfide, and therebyeffecting a continuous reaction between said phosphorus and said sulfurand continuous distillation of said reaction product in theform of aproduct having a bright yellow color, said phosphorus and said sulfurbeing introduced continuously into said boiling mass in substantiallythe proportions calculated to yield said phosphorus sulfide and at arate maintaining said mass in a boiling condition, and said boric oxideis introduced at a rate sufcient to produce said color improvement.

5. The method of claim 4, wherein the phosphorus sulde is phosphoruspentasulde andthe boric oxide is added at a rate not to exceed about 5percent by weight of the phosphorus and sulfur continuously added to theboiling mass of phosphorus pentasulde.

6. The method of claim 5, wherein about l percent of boric oxide isemployed.

7. A method of preparing bright yellow colored phosphorus suldes whichcomprises continuously introducing phosphorus, sulfurand boric oxideinto a boiling mass consisting of a phosphorus sulfide selected from thegroup consisting of phosphorus pentasulde, phosphorus heptasuliide andphosphorus sesquisulde, and thereby effecting a continuous reactionbetween said phosphorus and said sulfur and continuous distillation ofsaid reaction product in the formof a product having a bright yellowcolor, said phosphorus and said sulfur being introduced continuouslyinto said boiling mass in substantially the proportions calculated toyield said phosphorus sulfide and at a rate maintaining said mass in aboiling condition, and said boric oxide is introduced at a rate suicientto produce said color improvement.

No references cited.

1. A METHOD OF PREPARING BRIGHT YELLOW COLORED PHOSPHORUS SULFIDES WHICHCOMPRISES INTRODUCING BORIC OXIDE INTO A MASS OF DARKLY COLOREDPHOSPHORUS SULFIDE, AND SUBJECTING THE RESULTING PRODUCT TO DISTILLATIONTO SEPARATE SAID PHOSPHORUS SULFIDE IN THE FORM OF A PRODUCT HAVING ABRIGHT YELLOW COLOR, SAID BORIC OXIDE BEING EMPLOYED IN AN AMOUNTSUFFICIENT TO PRODUCE SAID COLOR IMPROVEMENT.